This section merely provides background information related to the present disclosure and may not constitute prior art.
Double wall tubing is conventionally used for various applications. For example, double wall tubing may be used for motor vehicle hydraulic fluids such as brake fluid. Many other applications for double wall tubing are known, including fuel lines, oil lines, heating and cooling units and the like.
Traditionally, double wall tubing may consist of a copper plated low carbon steel strip (as described in ASTM A-254 norm). The copper plated steel strip is rolled into a tubular form and subsequently brazed in a reducing atmosphere. Brazing can be achieved either by resistance welding, induction welding or furnace fusion welding. In order to achieve a proper joint, it is necessary to reach an approximate temperature of 1010° C. The layers fuse or solidify together as the temperature decreases.
Exposing low carbon steel based metal to a temperature range of 1010° C. to 1200° C. causes a metallurgical transformation known as recrystallization. This metallurgical transformation may negatively impact the grain size, as well as the overall mechanical properties of the steel. Consequently, these brazing conditions involving high temperatures greatly limit the range of steel grades suitable for use with double wall tubes.
While known double wall steel tubes and related methods of manufacturing double wall steel tubes have proven to be generally acceptable for their intended uses, a continuous need for improvement exists in the relative art.